A light-emitting diode (LED) is a semiconductor diode that emits light when an electrical current is applied in the forward direction of the device, such as in a simple LED circuit.
The device is fabricated from layers of silicon and seeded with atoms of phosphorus, germanium, arsenic or other rare-earth elements. The layers of the device are called the die and the junction between the materials is where the light is generated. The electricity enters from one side of the die and exits out the other. As the current passes through the LED device, the materials that makes up the junction react and light is emitted. LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. A LED is usually a small area (less than 1 mm2) light source, often with optics added to the chip to shape its radiation pattern and assist in reflection. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be infrared, visible, or ultraviolet.